[pianotech] Belly talk

[David Love]

I was thinking mostly about the bevel. There the closer the match to the crown of the assembly the better so that the mating occurs with the least amount of bending.  Some bevel is desirable.

Forcing the tail down is too. There, it's beneficial in helping to produce an overall dome shape to the assembly.

I don't follow the serpentine thing.

David Love
www.davidlovepianos.com
415.407.8320


Jim Ialeggio <jim at grandpianosolutions.com> wrote:

>David L said:
>
><Maybe Jim should clarify which crown he is referring to. I didn't think 
>he was referring to removing crown in the rim such that the bass end 
>would not have to be forced down once the treble end was clamped.
>
>My interest is:
>
>1st and foremost- a good glue joint surface. This is hard, to achieve in 
>such an inaccessible location, but possible.
>
>2- a simple plane is easier to machine accurately than a serpentine 
>plane(if you can call a serpentine thingee a plane)
>
>3- Not adding unneccessary stress to the board @ glue-down. Having said 
>that, by definition, in a small belly at least, the back is going to 
>have to be forced down, sometimes considerably. So there's not getting 
>out of this one without adding some stress. And thinking about it, maybe 
>just not that important at all...still considering this one.
>
>Thinking out loud regarding the glue-down stress in # 3 above, the way 
>this original rim is shaped, had to greatly accentuate the amount of 
>tail force down required. This because along the curved side of the rim, 
>the high treble and low bass are the low points of the crown. It seems 
>clear to me that they were trying to add stress to the board in shaping 
>it in the way they shaped it. I don't think the accentuated long bridge 
>crown actually adds anything in the way of stress induced stiffness to 
>the system anyway, but it seems clear that that is what they thought 
>they wanted to achieve.  Just to be clear, I don't buy the stress 
>induced stiffness scenario.
>
>Some stress is getting added...no way around it. But do I want to add 
>the amount of stress they had in mind. I don't think so, but as always, 
>I remain open to reasonable explanations to the contrary.
>
>HOwever, 1st and foremost, I want a good glue joint surface, and a good 
>glue surface on this difficult to access ledge, is a challenge. The 
>stress of glue-down while probably being ineffective at adding 
>stiffness, is quite effective at challenging the glue joint. Hence my 
>skepticism of making this joint more complex than it needs to be.
>
>I'm not sure where I come down on the beveled face of the inner rim glue 
>ledge. The existing was a full 5 deg, and had plastic resin filling and 
>leveling the joint in some spots, undoing some of the beveling.
>
>Jim Ialeggio
>
>-- 
>Jim Ialeggio	
>jim at grandpianosolutions.com
>978 425-9026
>Shirley Center, MA
>
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